Cataract is one of the most common causes of blindness. Approximately 20.5 million (17.2%) Americans have a cataract in either eye, and these numbers are rising. Cataract is most commonly seen between the ages of 45-64, with a lower prevalence in males than in females. Its symptoms are manifested by progressive cloudiness of crystalline lens of the eye, leading to glare, myopic shifts, monocular diplopia, and gradual loss of vision. The comorbidities are environmental conditions such as UV exposure, altitude, occupation, diet, smoking, alcohol, medication such as steroids and diseases such as ocular inflammation (uveitis) diabetes mellitus and hypertension, as side effects of x-ray radiation and in children traumatic eye injuries and genetic predisposition. The cataract is classified depending on the stage of the lens opacification as incipient, immature, and mature and hypermature, or the location of lens opacities as cortical, nuclear, posterior subcapsular.
The treatment for cataract is surgical removal of the involved lens and is achieved by various methods. It is done under a regional anesthesia, topical anesthesia, retrobulbar anesthesia and peribulbar anesthesia, etc.
One method of treatment is intracapsular cataract extraction (“ICCE”) in which the entire lens including the lens capsule is removed in one piece. This requires a relatively large 7-10 mm corneal incision through which the lens is expressed out of the eye. The procedure is seldom performed because of its numerous complications of corneal keratopathy, vitreous loss, wound leak, iris incarceration, high astigmatism, post-operative inflammation, cystoid macular edema, retinal detachment and high rate of the infection and corneal complications (bullous keratopathy). Following the operation, patients have been prescribed thick refractive glasses, which may be difficult to maintain on the patient's nose. The patients of this operation have been prone to falling when going down the stairs, and fractured bones were not an uncommon problem in these patients, even increasing the patient's mortality.
Another method of cataract treatment is extracapsular cataract extraction (“ECCE”), a procedure in which the lens cortex and nucleus is removed by an aspiration and irrigation system after removal of a part of the anterior capsule, while the rest of the capsule remains in place. This procedure has been performed most often in children having congenital cataract to avoid disrupting the posterior capsule to prevent vitreous loss. The surgery has been associated with serious post inflammatory response, glaucoma, proliferation of lens epithelial cells producing severe capsular opacification and fibrosis, and potentially retinal detachment when the posterior capsule has been inadvertently violated.
Yet another method of cataract treatment is extracapsular cataract extraction with phacoemulsification combined with intracapsular implantation of an acrylic intraocular lens (“IOL”). In this procedure, the lens cortex and nucleus are removed through a relatively small corneal incision, between about 4 mm to 5 mm in diameter, and an anterior capsulotomy. Then, an ultrasonically driven needle is used to emulsify the lens cortex and nucleus, which are then removed by an irrigation/aspiration of fluid and the lens cortical material. Subsequently, a folded IOL is implanted inside the lens capsule through a small corneal incision. While this concept has brought significant improvement to the technique of cataract surgery and benefit for the patient, the remaining lens epithelial cells have been found to attach to the anterior capsule, often proliferating posteriorly to produce a posterior capsular cloudiness and fibrosis which reduces post-operative visual acuity in the patient. Treatment of this complication involves either an yttrium aluminum garnet (“YAG”) laser capsulotomy, or the removal of the part of the posterior capsule with a vitrectomy instrument by cutting and removing central part of the posterior capsule and the vitreous in order to clear the optical media. This procedure has been done routinely in the developed countries, however, it is not easily done in developing countries with a large cataract population because of the cost of a YAG-laser and/or the difficulty for the patient to return to a surgery center for an additional surgery.
An alternative procedure is to perform a limited central anterior and posterior capsulotomy in a single procedure, and the lens optic is implanted in the space of Berger located between the posterior lens capsule and anterior hyaloid membrane, while the lens haptics remain substantially in front of the lens capsule located in the posterior chamber contacting the ciliary body. When done properly, this procedure leaves a clear optical media in one surgical session without the need for subsequent need for the posterior capsulotomy. The lens capsule folds upon itself in this procedure.
In general, IOL implantation has a decades long history of biocompatibility in the eye. The IOLs are made from polymeric materials such as PMMA, silicone, hydrogel, polyvinylidene fluoride, or in combination with collagen as Collamer, multifocal IOLs are effective in providing near and far vision after cataract surgery. Toric IOLs are used to correct corneal astigmatism, such as the Alcon acrylic toric IOLs or the Johnson and Johnson Tecnis Toric 1-piece IOL.
Despite the advances in cataract surgery and the construction of the new IOLs, there are still some problems the patients have to deal with, that affect their visual satisfaction in the post-operative period.
For example, the IOLs can tilt either in a horizontal or vertical direction inducing great dissatisfaction for the patient. This happens frequently if the capsulotomy is not done properly or the lens zonulas are genetically affected in diseases such as in patients with Marfan syndrome, Morgagnian cataract, high myopia, or after traumatic injuries where the zonulas can become weak or broken, and the incomplete or partial lens zonulae contribute to a tilted IOL.
The IOLs can tilt or settle in the post-operative period as a result of capsular fibrosis after cataract surgery, for example, if the haptic and optics are inside the capsular bag and an uneven pressure is generated as a result of capsular fibrosis or a large capsulotomy.
IOLs seldom have a perfect refractive power to create an emmetropic refraction after surgery. In majority of cases the IOLs refractive power is off by plus or minus 0.5 D power or more, which is not easy to correct if the IOLs are multifocal lenses.
Lens centration is very important for multifocal lenses, otherwise patients are not satisfied with their vision and a lens exchange may be needed.
Children's eyes and myopic eyes grow significantly, requiring removal of the IOL and their replacement.
Capsular opacification occurs after the cataract surgery when the lens epithelial cells, located behind the anterior capsule, start proliferating inside the lens capsule to fill the empty space left inside the capsule after cataract extraction while the post-operative inflammatory response persists.
A need remains for a patient to have only a single operation to correct the patient's vision over the lifetime of the patient, even for patients that are infants or minors.